1 package org.apache.turbine.util.pool;
2
3 /* ====================================================================
4 * The Apache Software License, Version 1.1
5 *
6 * Copyright (c) 2001 The Apache Software Foundation. All rights
7 * reserved.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 *
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 *
16 * 2. Redistributions in binary form must reproduce the above copyright
17 * notice, this list of conditions and the following disclaimer in
18 * the documentation and/or other materials provided with the
19 * distribution.
20 *
21 * 3. The end-user documentation included with the redistribution,
22 * if any, must include the following acknowledgment:
23 * "This product includes software developed by the
24 * Apache Software Foundation (http://www.apache.org/)."
25 * Alternately, this acknowledgment may appear in the software itself,
26 * if and wherever such third-party acknowledgments normally appear.
27 *
28 * 4. The names "Apache" and "Apache Software Foundation" and
29 * "Apache Turbine" must not be used to endorse or promote products
30 * derived from this software without prior written permission. For
31 * written permission, please contact apache@apache.org.
32 *
33 * 5. Products derived from this software may not be called "Apache",
34 * "Apache Turbine", nor may "Apache" appear in their name, without
35 * prior written permission of the Apache Software Foundation.
36 *
37 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
38 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
39 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
40 * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
41 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
42 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
43 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
44 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
45 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
46 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
47 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
48 * SUCH DAMAGE.
49 * ====================================================================
50 *
51 * This software consists of voluntary contributions made by many
52 * individuals on behalf of the Apache Software Foundation. For more
53 * information on the Apache Software Foundation, please see
54 * <http://www.apache.org/>.
55 */
56
57 /***
58 * Efficient array-based bounded buffer class.
59 * Adapted from CPJ, chapter 8, which describes design.
60 * Originally written by Doug Lea and released into the public domain.
61 * <p>[<a href="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html"> Introduction to this package. </a>] <p>
62 *
63 * @author <a href="mailto:ilkka.priha@simsoft.fi">Ilkka Priha</a>
64 * @version $Id: BoundedBuffer.java,v 1.1.1.1 2001/08/16 05:09:59 jvanzyl Exp $
65 */
66 public class BoundedBuffer
67 {
68 /***
69 * The default capacity.
70 */
71 public static final int DEFAULT_CAPACITY = 1024;
72
73 protected final Object[] array_; // the elements
74
75 protected int takePtr_ = 0; // circular indices
76 protected int putPtr_ = 0;
77
78 protected int usedSlots_ = 0; // length
79 protected int emptySlots_; // capacity - length
80
81 /***
82 * Creates a buffer with the given capacity.
83 *
84 * @param capacity the capacity.
85 * @throws IllegalArgumentException if capacity less or equal to zero.
86 */
87 public BoundedBuffer(int capacity)
88 throws IllegalArgumentException
89 {
90 if (capacity <= 0)
91 throw new IllegalArgumentException();
92
93 array_ = new Object[capacity];
94 emptySlots_ = capacity;
95 }
96
97 /***
98 * Creates a buffer with the default capacity
99 */
100 public BoundedBuffer()
101 {
102 this(DEFAULT_CAPACITY);
103 }
104
105 /***
106 * Returns the number of elements in the buffer.
107 * This is only a snapshot value, that may change
108 * immediately after returning.
109 *
110 * @return the size.
111 */
112 public synchronized int size()
113 {
114 return usedSlots_;
115 }
116
117 /***
118 * Returns the capacity of the buffer.
119 *
120 * @return the capacity.
121 */
122 public int capacity()
123 {
124 return array_.length;
125 }
126
127 /***
128 * Peeks, but does not remove the top item from the buffer.
129 *
130 * @return the object or null.
131 */
132 public synchronized Object peek()
133 {
134 if (usedSlots_ > 0)
135 return array_[takePtr_];
136 else
137 return null;
138 }
139
140 /***
141 * Puts an item in the buffer only if there is capacity available.
142 *
143 * @param item the item to be inserted.
144 * @return true if accepted, else false.
145 */
146 public synchronized boolean offer(Object x)
147 {
148 if (x == null)
149 throw new IllegalArgumentException();
150
151 if (emptySlots_ > 0)
152 {
153 --emptySlots_;
154 array_[putPtr_] = x;
155 if (++putPtr_ >= array_.length)
156 putPtr_ = 0;
157 usedSlots_++;
158 return true;
159 }
160 else
161 return false;
162 }
163
164 /***
165 * Polls and removes the top item from the buffer if one is available.
166 *
167 * @return the oldest item from the buffer, or null if the buffer is empty.
168 */
169 public synchronized Object poll()
170 {
171 if (usedSlots_ > 0)
172 {
173 --usedSlots_;
174 Object old = array_[takePtr_];
175 array_[takePtr_] = null;
176 if (++takePtr_ >= array_.length)
177 takePtr_ = 0;
178 emptySlots_++;
179 return old;
180 }
181 else
182 return null;
183 }
184 }
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